The present invention relates to a pivot joint for use particularly in automobile steering systems. xe2x80x9cAutomobilexe2x80x9d is understood to include cars, trucks and tractors as well as any type of industrial vehicle such as a works vehicle. Although the pivot joint of the present invention has widespread use in this application, it will be understood that such a pivot joint can be used for other applications without going outside the scope of the invention.
It is known that pivot joints may be subjected to significant stress and that they must be totally reliable, particularly when used in automobile steering systems. High quality parts are therefore needed. The resulting high material and production costs are reflected in the selling price.
This type of pivot joint is particularly disclosed in French patent FR 2,560,140. The joint essentially comprises a housing with a housing shank made as a single part, a pivot that has a head mounted within an opening in the housing, upper and lower bushings, a spring that presses the upper bushing against the head of the pivot and hence against the lower bushing.
Although the bushings are described as xe2x80x9cupperxe2x80x9d and xe2x80x9clowerxe2x80x9d, it is clear that this labeling is arbitrary and refers to their relative positions in the drawing; the names are only for convenience in describing the invention.
An inevitable problem with this type of pivot joint is the wear due to friction between the head of the pivot and/or the lower bushing. Indeed, in operation the pivot head rotates inside the housing formed by the bushings. There is therefore virtually imperceptible but continuous abrasion that wears away the head of the pivot and/or the lower bushing to the point where the pivot is no longer spherical. The loss of material gives rise to play that is fortunately directly compensated for when the upper bushing is activated by the spring. The upper bushing therefore acts to make up the play as the head of the pivot and/or the lower bushing are worn away. This type of wear is thus a well known problem. But in practice the state of wear is not easy to check. A very simple technique used by engineers consists in grasping the shaft on which the joint head is mounted and moving it so that the head moves in its housing. However, it is very difficult to establish the state of wear of the head by using this purely empirical technique since it is difficult to establish whether there is in fact play in the head or whether the head moving in its housing is due to the upper bushing moving against its spring. It is therefore very tricky to establish whether a pivot joint is still fit for use. This type of pivot joint can often be in an unacceptable state of wear that can cause an accident; conversely, pivot joints are often replaced when they are still perfectly capable of functioning.
British patent GB 1,336,087 discloses a pivot joint the upper bushing of which comprises a greasing unit consisting of a bush 38 that projects from the housing of the pivot. This bushing is pressed elastically against the head of the pivot by a compressed elastomer ring. This ring bears both on the movable upper bushing and a fixed cover 28. The cover is pierced by an aperture 40 through which the bush 38 of the bushing projects. Consequently as the head of the pivot wears away, the bush is pushed into the aperture, thereby giving an indication of the wear on the head and/or the lower bushing.
The design of this pivot joint is outmoded as it requires greasing. Modern pivot joints are permanently lubricated and require no greasing unit. As the fixed cover 28 serves to seal the housing, the presence of an aperture would be harmful.
The present invention aims to overcome this drawback in the prior art by disclosing a pivot joint of modern design for which it is very easy to determine whether it is still capable of fulfilling its function.
To do this, a first embodiment of the present invention proposes a pivot joint, particularly intended for automobile steering systems, that comprises a housing and a pivot head lodged inside said housing, said pivot head consisting of a spherical head constructed as part of a shank that projects through an aperture in the housing, a lower bushing that forms a lower bearing seat enclosing the head of the pivot on the open side of the housing and an opposite movable upper bushing that forms an upper bearing seat, said upper bushing being pressed by a spring against the head of the pivot so that it is moved towards the lower bushing as the pivot head wears, said pivot joint comprising means for indicating the wear of the head of the pivot capable of giving an indication of the wear of said head relative to the movement of said upper movable bushing, said wear indicator means comprising a contact component capable of coming into contact with a part of said upper movable bushing, the contact component being disposed in the path of translational movement of said upper bushing towards said lower bushing.
Given that it is difficult to measure the wear on the head of the pivot directly in terms of the reduction of its radial diameter, it was necessary to use a parameter that was dependent on this wear but which was easier to determine. By using the displacement of the upper bushing it was possible to replace a radial magnitude by an axial magnitude that is easier to measure.
In a second embodiment, the invention proposes a pivot joint, particularly intended for automobile steering systems, that comprises a housing and a pivot head lodged inside said housing, said pivot head consisting of a spherical head constructed as part of a shank that projects through an aperture in the housing, a lower bushing that forms a lower bearing seat enclosing the head of the pivot on the open side of the housing and an opposite movable upper bushing that forms an upper bearing seat, said upper bushing being pressed by a spring against the head of the pivot so that it is moved towards the lower bushing as the lower bushing wears, said pivot joint comprising means for indicating the wear of the lower bushing capable of indicating the wear of the said bushing, said wear indicator means comprising a contact component capable of coming into contact with head of the pivot activated by the spring.
The same principle is used in this embodiment, i.e. a component is positioned in the displacement path of a component of the joint that moves under the effect of wear. In this embodiment, which applies more particularly to joints subject to wear on the lower bushing, it is the head of the pivot that constitutes the movable component designed to come into contact with the contact component of the wear indicator means. It is clear that this second embodiment would be inefficient for joints in which the lower bushing does not wear.
In a first type of embodiment the indicator means provide an electrical indication that can be displayed as an indicator lamp.
In a second type of embodiment the indicator means provide a discrete visual indication that represents a value of the acceptable limit of wear.
In another version, the indicator means give a continuous visual display that represents the progressive wear of the head.
Advantageously the contact component is fastened to a component that conducts electricity and is capable of establishing an electrical contact when the contact component is activated by the head or the upper bushing.
In a second type of embodiment the contact component comprises the surface of a cam designed to slide against part of the upper bushing, thereby causing the said contact component to move in translation in a direction perpendicular to the direction of displacement of said upper bushing.
In a third type of embodiment the contact component comprises an endpiece designed to break under the effect of the said upper bushing or head, said endpiece being connected to a shank, a spring drawing said shank away from said endpiece such that the breakage of said component frees said shank.
In another type of embodiment the said contact component is maintained in the path of displacement of the upper bushing or the head by a connection designed to break when it comes into contact with the upper bushing or the head.
Other characteristics of the present invention will be better understood from the following description of a non-limitative example. The description refers to the attached figures and will make it clear how the invention may be embodied.